The above words in latency heat maps are from http://dtrace.org/blogs/brendan/2009/03/17/heat-map-analytics/ where there is information on heat maps.In the graphic at the top of the page I put lgwr in an I/O write throttle group and played with the I/O throttle. I was running a swingbench load and at the same as throttling I/O such that latencies started off good then got worse and then back to normal.The full steps are:

Run an auto refresh color coded heatmap on “log file sync” in sqlplus by typing

See Brendan Gregg’s blog on how important and cool heatmaps can be for showing latency information and how average latency hides what is really going on:
Now if we want to create heatmap graphics, how can we do it? Two popular web methods for displaying graphics are Highcharts and D3. Two colleges of mine whipped up some quick examples in both Highcharts and D3 to show latency heatmaps and those two examples are shown below. The data in the charts is random just for the purposes of showing examples of these graphics in actions.